3D printing of bio-inspired, multi-material structures to enhance stiffness and toughness

In nature, many biological, multi-materials have complex microstructures and excellent mechanical properties. One shellfish material called nacre has received much attention due to its unique interlocking structure of alternating calcium carbonate tablet and soft organic matter filler. It has microstructure features such as waviness which provide high strength and toughness properties. As a popular topic in the study of bio-inspired structure, it is of great significance to study the ordered microstructure and toughening mechanism of nacre. 3D printing allows for the easy manufacture of complex structures. In this project, inspired by the high strength and toughness of natural nacre, 3D printing technology was used to prepare nacre-like, multi-material structure. Tensile tests, cyclic tensile test and fracture toughness tests were carried out to investigate the relationship between multi-material structure geometry and tensile properties, fracture modes and toughness behaviour. In the experimental part of this thesis, specimens of the tablet-filler with different dovetail angles made by polylactic acid (PLA) and thermoplastic polyurethane (TPU) inspired by the microstructure of nacre structure were prepared through Fused filament fabrication (FFF)/ Fused Deposition Modelling (FDM) type of 3D printing technology. The multi-material dovetail PLA & TPU specimens exhibited multi-stage deformation under tensile testing. By comparing the tensile performance of structure made by dovetail PLA & PLA material as well as unidirectional pure PLA specimen, it was confirmed that the incorporation of soft TPU filler gave the opportunity for tablet sliding, resulting in a complex multi-stage deformation mechanism of the structures. Two modes of failure mechanisms, tablet pull-out and tablet break, were observed for the multi-material PLA & TPU structure under tensile testing. The combination of tablet break and pull-out modes can lead to higher strength and modulus than tablet pull-out. In the tablet pull-out mode, transverse expansion was observed in the larger angle dovetail structure, and the occurrence of negative Poisson's ratio effect was determined by calculation. In addition, there is a distinct plateau stage in the tensile curve of multi-material PLA & TPU structure, through cyclic tensile tests identified the plateau as a yield point, generated by short interface between tablets and filler broken. The cyclic tensile tests also determined that the main deformation resistance of the PLA & TPU structure was provied by the long interface broken between tablets and filler, also the interlocking and shearing between the dovetail angle tablets. Multi-material PLA & TPU structures with larger dovetail angles produced greater plastic deformation and absorbed more energy during tensile testing. Multi-material PLA & TPU with 5˚ dovetail showed the highest ultimate tensile strength 11.46 MPa and Young’s modulus of 495.96 MPa, but 9˚ dovetail performed poorly with 6.51 MPa and 395.48 MPa, respectively. The value even below than 1˚ dovetail (ultimate tensile strength of 9.82 MPa, modulus of 453.38 MPa). The ultimate tensile strength and Young’s modulus of the multi-material PLA & TPU structure are not as high as those of unidirectional pure PLA and dovetail PLA & PLA specimen, but energy absorption performance is improved by soft TPU filler and dovetail angles. In fracture experiments, crack extension behaviour was observed in fracture toughness specimens. In summary, the mechanical properties of the nacre-like, multi-material structure were investigated by tensile behavior, fracture mode and energy absorption analysis in this paper. It is demonstrated that the combination of stiff tablet material and soft filler material can effectively improve the toughness of the structure. The tensile strength of the multi-material structure can be improved by increasing the dovetail angle of the tablet. However, it has not been observed that increasing the dovetail angle can significantly increase stiffness. It is confirmed that the optimized design of the 3D printed, bio-inspired, multi-material structure can change the mechanical behavior of the structure and improve its mechanical properties, can provide new ideas for the development of composite materials with excellent mechanical properties.

Endoscopic Hemostatic Treatment with a Novel Self-Assembling Peptide Gel for Precut Fistulotomy-Related Bleeding

Introduction: Precut fistulotomy is of interest as one of the salvage techniques for selective bile duct cannulation using endoscopic retrograde cholangiopancreatography. Of the various endoscopic treatments reported to date for bleeding associated with papillotomy incision, endoscopic hemostasis treatment with a novel self-assembling peptide (SAP) matrix-forming gel (TDM-621) (3-D Matrix Ltd., Tokyo, Japan) remains only insufficiently reported in the literature. Case Presentation: We herein report 6 cases of precut fistulotomy-related bleeding successfully treated with endoscopic hemostasis treatment with TDM-621, i.e., 5 and 1 cases during and after precut fistulotomy, respectively, in 2 males and 4 females aged 68–96 years (mean age, 85 years), 3 of whom had been on antithrombotic drugs. Types of bleeding treated included oozing bleeding (n = 5) and oozing bleeding from a visible vessel (n = 1). In all cases, complete hemostasis was achieved with TDM-621 without causing rebleeding. Conclusion: Endoscopic hemostasis with TDM-621 may prove effective for precut fistulotomy-related bleeding and represent a potential modality of first choice in hemostasis. In addition, endoscopic hemostasis with combined modality therapy using TDM-621 and endoscopic hemoclips may prove effective for bleeding from visible vessels

Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years

Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.Comment: 17 pages, 15 figures, 2 tables, refereed version. For associated data files, see https://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/523/219

Primary adenomyoepithelioma of tonsil

We present a case of adenomyoepithlioma (AME) arising from the tonsil. AME is an uncommon tumor that typically arises in breast, but rarely found in salivary glands, lung, and skin. Its biological features have not been thoroughly characterized. Here we describe a primary AME originating from the tonsil. The pathologic changes were characterized by hypercellularity, the dominance of both epithelial and myoepithelial cells. Malignancy was evidenced by the presence of a high mitotic rate and invasive growth. The epithelial cells express high levels of cytokeratin and epithelial membrane antigen (EMA). The myoepithelial cells show positive staining for calponin, p63, vimentin, and S-100. A thorough review of the literature indicates that this is likely the first reported case of AME from the tonsil. Following descriptions of the diagnosis, treatment, and prognosis of this specific case, pathologic and clinical characteristics of AME from other tissues are also compiled and discussed

SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features

We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d ≈ 16.2 Mpc) starting 10 hr after explosion and continuing for ~300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRT–discovered X-ray emission (L_x ≈ 10⁴¹ erg s⁻¹ at 3 days; L_x ∝ t⁻³), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v ≈ 500 km s⁻¹) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r (0.1–1) × 10¹⁷ cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of t_r = 13.4 ± 0.210 days and a peak B-band magnitude of M_B = −15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) × 10⁻² M_⊙ of ⁵⁶Ni and ejected M_(ej) = (0.72 ± 0.040) M⊙ total with a kinetic energy E_k = (1.8 ± 0.10) × 10⁵⁰ erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (~10 M_⊙) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries

Role of Na/H exchange in insulin secretion by islet cells

PURPOSE OF REVIEW: Sodium/hydrogen exchangers (NHEs) are a large family of transport proteins catalyzing the exchange of cations for protons across lipid bilayer membranes. Several isoforms are expressed in β cells of the endocrine pancreas, including the recently discovered and poorly characterized isoform NHA2. This review will summarize advances in our understanding of the roles of NHEs in the regulation of insulin secretion in β cells. RECENT FINDINGS: Plasmalemmal full-length NHE1 defends β cells from intracellular acidification, but has no role in stimulus-secretion coupling and is not causally involved in glucose-induced alkalinization of the β cell. The function of a shorter NHE1 splice variant, which localizes to insulin-containing large dense core vesicles, remains currently unknown. In contrast, in-vitro and in-vivo studies indicate that the NHA2 isoform is required for insulin secretion and clathrin-mediated endocytosis in β cells. SUMMARY: Recent data highlight the importance of NHEs in the regulation of cellular pH, clathrin-mediated endocytosis and insulin secretion in β cells. Based on these studies, a pathophysiological role of NHEs in human disorders of the endocrine pancreas seems likely and should be investigated